The present invention relates to a method of handling, in particular depressurizing, a solvent-containing solids stream in a non-aqueous oil sand extraction process (i.e. using a non-aqueous solvent).
Various methods have been proposed in the past for the recovery of bitumen (sometimes referred to as “tar” or “bituminous material”) from oil sands as found in various locations throughout the world and in particular in Canada such as in the Athabasca district in Alberta and in the United States such as in the Utah oil sands. Typically, oil sand (also known as “bituminous sand” or “tar sand”) comprises a mixture of bitumen (in this context also known as “crude bitumen”, a semi-solid form of crude oil; also known as “extremely heavy crude oil”), sand, clay minerals and water. Usually, oil sand contains about 5 to 25 wt. % bitumen (as meant according to the present invention), about 1 to 13 wt. % water, the remainder being sand and clay particles.
As an example, it has been proposed and practiced at commercial scale to recover the bitumen content from the oil sand in an extraction process by mixing the oil sand with water and separating the sand from the aqueous phase of the slurry formed.
Other methods have proposed non-aqueous extraction processes (i.e. using a non-aqueous solvent) to reduce the need for large quantities of process water.
A problem of known methods of non-aqueous extraction of bitumen from oil sand is the handling of solvent-containing solids streams and in particular the removal of the non-aqueous solvent from the solids. Significant amounts of heat would be needed to evaporate the non-aqueous solvent. Also, if a pressure-filtration step (i.e. applying pressure above the filter bed during filtration) would be used during filtration this may create issues with respect to depressurizing the pressurized stream (viz. the processed filter cake that has been removed from the filter), which would typically take place in a rotary valve or lock hopper, which devices are expensive and sensitive to wear.
It is an object of the present invention to improve the handling, in particular depressurizing, of solvent-containing solids streams.
It is a further object of the present invention to avoid or at least minimize the issue of handling, in particular depressurizing, a pressurized solvent-containing solids stream, in particular obtained after a filtration step in a non-aqueous oil sand extraction process.
One or more of the above or other objects may be achieved according to the present invention by providing a method of handling a solvent-containing solids stream in a non-aqueous oil sand extraction process, the method comprising at least the steps of:
(a) providing a solvent-containing solids stream at a first pressure;
(b) depositing the solvent-containing solids stream provided in step (a) as a bed in a vessel;
(c) discharging the solvent-containing solids stream from the vessel at a second pressure via an outlet, thereby obtaining a depressurized solvent-containing solids stream;
wherein the solvent-containing solids stream in the vessel in step (b) is at a temperature above the boiling point of the solvent in the depressurized solvent-containing solids stream at the second pressure in step (c).
It has now been found that the method according to the present invention provides a surprisingly simple and elegant manner to handle solvent-containing solids streams in an oil sand extraction process using a non-aqueous solvent. The method according to the present invention is, although not limited thereto, of particular use in handling, in particular depressurizing, a pressurized solvent-containing solids stream (such as the heated filter cake obtained in a pressure-filtration step) in a non-aqueous oil sand extraction process.
An advantage of the present invention is that very simple outlet devices such as cone valves can be used. There is no need to use more complicated outlet devices such as rotary star valves or lock hoppers. When using rotary star valves, pressure barriers are established by valve compartments separated by the valve vanes of the rotary star valve (according to the present invention, the bed of solvent-containing solids functions as a pressure barrier). Such rotary star valves are expensive, sensitive to wear and maintenance-intensive. Also, replacement of such rotary star valves may take a long time.
The person skilled in the art is familiar with a non-aqueous oil sand extraction process; hence this will not be described here in further detail. Typically, a non-aqueous oil sand extraction process comprises at least the steps of:
reducing the oil sand ore in size, e.g. by crushing, breaking and/or grinding, to below a desired size upper limit (such as for example 20 inch);
contacting the oil sand with a non-aqueous solvent, thereby obtaining a solvent-diluted oil sand slurry;
filtering the solvent-diluted oil sand slurry (whilst possibly applying pressure-filtration), thereby obtaining a solids-depleted stream and a solids-enriched stream (‘filter cake’); and
removing solvent from the solids-depleted stream obtained thereby obtaining a bitumen-enriched stream that can be further processed to obtain the bitumen. The bitumen may subsequently be further processed in e.g. a refinery.
The method according to the present invention is of particular use for depressurizing a solvent-containing solids stream (i.e. the ‘filter cake’ as mentioned above) after a pressure-filtration step.
In step (a) a solvent-containing solids stream is provided at a first pressure. As mentioned above, the solvent-containing solids stream is obtained in a non-aqueous oil sand extraction process (i.e. using a non-aqueous solvent) and is preferably obtained in a pressure-filtration step in the non-aqueous oil sand extraction process.
The solvent as used in the method of the present invention may be selected from a wide variety of non-aqueous solvents (although a small amount of water may be present), aromatic hydrocarbon solvents and saturated or unsaturated aliphatic (i.e. non-aromatic) hydrocarbon solvents; aliphatic hydrocarbon solvents may include linear, branched or cyclic alkanes and alkenes and mixtures thereof. Preferably, the solvent comprises an aliphatic hydrocarbon having from 3 to 9 carbon atoms per molecule, more preferably from 4 to 7 carbons per molecule, or a combination thereof. Especially suitable solvents are saturated aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, octane and nonane (including isomers thereof), in particular butane, pentane, hexane and heptanes, preferably pentane. It is preferred that the solvent in step (a) comprises at least 50 wt. %, preferably at least 90 wt. % of the aliphatic hydrocarbon having from 3 to 9 carbon atoms per molecule, more preferably at least 95 wt. %. Also, it is preferred that in step (a) substantially no aromatic solvent (such as toluene or benzene) is present, i.e. less than 5 wt. %, preferably less than 1 wt. %. Further it is preferred that a single solvent is used as this avoids the need for a distillation unit or the like to separate solvents. Also, it is preferred that the solvent has a boiling point lower than that of the bitumen to facilitate easy separation and recovery.
As mentioned above, the solvent-containing solids stream provided in step (a) is preferably a filter cake obtained in the oil sand extraction process.
Preferably, the solvent-containing solids stream provided in step (a) contains from 1.0 wt. % to 20 wt. % solvent. Preferably, and in particular when the solvent is pentane, the solvent-containing solids stream provided in step (a) contains from 2.0 wt. % to 15 wt. % solvent, preferably at least 3.0 wt. %, more preferably at least 4.0 wt. % and preferably at most 12 wt. %, more preferably at most 10 wt. %, based on the weight of the solids in the solvent-containing solids stream.
Further it is preferred, that the solvent-containing solids stream provided in step (a) contains from 2.0 wt. % to 10 wt. % water, preferably at least 3.0 wt. % and preferably at most 7.0 wt. %, based on the weight of the solids in the solvent-containing solids stream.
Also it is preferred, that the solvent-containing solids stream provided in step (a) contains from 0.1 wt. % to 10 wt. % bitumen, preferably at least 0.2 wt. %, more preferably at least 0.3 wt. % and preferably at most 2.0 wt. %, more preferably at most 1.5 wt. %, based on the weight of the solids in the solvent-containing solids stream.
Typically, the solvent-containing solids stream provided in step (a) contains from 79.0 wt. % to 97.0 wt. % solids, preferably at least 85.0 wt. %, more preferably at least 88.0 wt. %, and preferably at most 96.0 wt. %, more preferably at most 94.0 wt. %.
Typically, the first pressure in step (a) is at an elevated level and equal to or slightly above the vapour pressure of the solvent-containing solids stream. Preferably and in particular when the solvent is pentane, the solvent-containing solids stream provided in step (a) has a (first) pressure from 1.5 bara to 6.0 bara, preferably at least 2.0 bara and preferably at most 5.0 bara.
Also, the solvent-containing solids stream provided in step (a) is typically at an elevated temperature. Preferably, and in particular when the solvent is pentane, the solvent-containing solids stream provided in step (a) has a temperature from 50° C. to 100° C., preferably at least 60° C. and preferably at most 90° C.
In step (b), the solvent-containing solids stream provided in step (a) is deposited as a bed in a vessel. The person skilled in the art will readily understand that the vessel is not limited in any way. Typically, the vessel is selected such that the discharge (in step (c)) of the solvent-containing solids stream through a bottom outlet is facilitated. Preferably the bed of solvent-containing solids is not supported (by a grid, mesh or the like) as this would hamper the subsequent discharge of the solvent-containing solids.
In step (c), the solvent-containing solids stream is discharged from the vessel at a second pressure via an outlet, thereby obtaining a depressurized solvent-containing solids stream. The second pressure (in step (c)) is at a lower pressure than the first pressure (in step (a)).
Preferably, the depressurized solvent-containing solids stream obtained in step (c) has a pressure from 0.8 bara to 1.5 bara, preferably from 0.9 bara to 1.2 bara.
Further it is preferred that, in particular when the solvent is pentane, the depressurized solvent-containing solids stream obtained in step (c) has a temperature from 40° C. to 60° C., preferably at least 45° C. and preferably at most 55° C.
The person skilled in the art will readily understand that the outlet of the vessel may have various sizes and shapes and may be at various locations in the vessel, as long as a bed of solids is present between the inlet and the outlet of the vessel. Preferably, the outlet as used in step (c) is a bottom outlet. Preferably, the bottom outlet comprises a cone valve. Suitable cone valves can be obtained from e.g. ISL Cone Valve Technology (Moreton in Marsh, UK).
Further it is preferred that the upper level of the bed of solvent-containing solids in the vessel is maintained between a preselected upper limit and lower limit. This, to ensure that a suitable pressure barrier is created between the solvent-containing solids stream at the first pressure and the depressurized solvent-containing solids stream at the second pressure. Also, the bed avoids or at least minimizes a vapour slip stream through the bed. This maintaining of the level of the bed may be done by for example using a cone valve discharge opening and properly adjusting the cross-sectional area of the cone valve discharge opening.
The person skilled in the art will readily understand that the depressurized solvent-containing solids stream obtained in step (c) may be further processed to separate the solvent vapour from the solids, e.g. using a vessel, cyclone, scrubber or the like.